In the case of a needleless syringe with which the injection is performed without using an injection needle, such a construction is adopted that an injection component is discharged by applying the pressure to an injection solution containing a medicament or the like by means of a pressurized gas or a spring. The pressurizing force, which is applied to the injection solution, is adjusted so that the injection solution can be delivered to an intended area in the living body. In this context, the ability, which makes it possible to administer the medicament to Langerhans cells in the skin, is especially remarked when the medicament is injected into the living body by using, for example, the needleless syringe. Langerhans cells are dendritic cells ordinarily existing in the upper stratum spinosum of the skin. It is known that the cells relate to the immune response of the skin, and the cells migrate from the skin to the lymph node. The cells have the common receptor for macrophage, and the cells function as the antigen-presenting cells for T lymphocyte and B lymphocyte. Therefore, Langerhans cells are especially important in the acceleration of vaccine development and the research on the immune system relevant to the treatment to prevent and cure the autoimmune disease and the rejection symptom. However, Langerhans cells exist at a relatively shallow region of the skin. Therefore, the efficient execution of the administration of the injection solution to Langerhans cells is extremely effective for the needleless syringe which does not have any injection needle for directly carrying the injection solution to the inside of the living body.
On the other hand, Patent Document 1 discloses such a technique that the shallow intradermal injection into the region in which Langerhans cells exist can be achieved. According to the technique, the interior of a syringe is allowed to be in a vacuum state by means of suction generating means to form a state in which the skin tissue is pressed against an orifice from which the injection solution is discharged. The injection solution is discharged with a jet flow having a velocity sufficient to cause the permeation into the pressed skin tissue.